This invention relates to the improvement in the stalling aerodynamics of the Cessna Models 150 and 152 series aircraft by the assembly of stall strips on the leading edges of the wings adjacent to the wing roots of these aircraft. The proper size and location of these strips were determined through flight testing to obtain the desired results for the particular series of light aircraft.
While the requirements of all flight instruction include the techniques for recovery from stalls and spins, the incidence of accidents caused by stalls and spins is a source for concern with Government agencies such as the Federal Aviation Agency and the National Transportation Safety Board. The stall/spin accident statistics accumulated by the Federal Aviation Administration and the National Transportation Safety Board on the Cessna 150 and 152 indicate that an improvement to the basic aircraft is needed. A published table derived from the 1977 FAA "Analysis of Selected General Aviation Stall-Spin Accidents" ranks the Cessna 150 fourth in the number of stall/spin accidents per 1,000 aircraft out of a group of thirty-six different aircraft. The National Transportation Safety Board has stated that the Cessna 150 has a "very high" stall/spin frequency and their recommendations have called for "modification kits aimed at improving the handling characteristics of present aircraft" (Reference NTSB-AAS-72-8, "Special Study, General Aviation Stall/Spin Accidents" adopted Sept. 13, 1972). The Cessna 150/152 series aircraft has been produced for over twenty years without successful improvement in handling characteristics to overcome the inherent aerodynamic difficulties in a stall/spin condition. Therefore, the need exists for a modification to the airplane wings of the Cessna 150 and 152 which minimizes the dangers of loss of control from stall or spin when the flying conditions would otherwise so generate the same.
An aircraft is in a stalled condition when the airflow passing over the upper wing surface is no longer flowing smoothly, but has become separated or detached from the wing's surface. This occurs at a given angle of attack of the wing section relative to the wing's flight path. That portion of the wing which has separated airflow is no longer producing lift. This occurs at the lowest speed capability of the aircraft with the aircraft under a normal one gravity acceleration, i.e. the stall speed.
Heretofore, since the point at which the stall occurs is dependent on the angle of attack for a given airfoil section, it has been the normal design practice to put a twist in the wing. This is done so that the wing tip is flying at a lower angle of attack than the wing root. Thus, the stall (separated airflow) will originate at the wing root and progress towards the wingtip. A wing without wing twist could stall simultaneously along the whole wing panel and the aircraft could easily roll off into spin entry because the ailerons for controlling the roll have also stalled. Thus, it has been a normal design practice to build a 21/2 to 3 degree twist in the wing at the time of the wing's manufacture on most general aviation aircraft to provide for an acceptable stall progression on the wing.
The Cessna Models 150 and 152 have only a one degree twist in the wing, with the wing tip flying at an angle of attack of one degree less than the wing root. Since the point at which the stall occurs is dependent on the angle of attack, the outer wing panel, having the ailerons, is not sufficiently protected from stalling when the wing root stalls. Pilots who place the aircraft in a yaw by improperly using the rudder pedals and the opposite aileron to pick up the falling wing, otherwise known as cross controlling, can cause one whole wing panel, that which has the downward deflected aileron and pro-spin rudder, to stall out when the stall occurs. If this happens, the aircraft will roll off into a spin entry. Therefore, a modification, in addition to wing twist, is necessary for Cessna Models 150 and 152 series aircraft which provide acceptable stall characteristics to satisfy the recommendation of the National Transportation Safety Board.